1. Field of the Invention
The present invention relates to pressable explosive compositions with enhanced sensitivity characteristics and processability.
2. Background
RDX and HMX are crystalline explosive compounds, whose use has been known in the field of military pressable explosive compounds for a number of years. Pressable explosive compositions are traditionally employed for making charges for use in ammunition.
The breakthrough came when in 1925 G. C. Hale described a detailed process for producing RDX by means of 99.8% nitric acid and hexamine. HMX was discovered a few years later when the use was introduced of acetic anhydride for increasing the RDX yield (the Bachmann process) where HMX was basically regarded as a by-product. After the Second World War a great deal of work was done in order to guide the process in the direction of increased yields of HMX and RDX.
Several types of RDX exist. Two of these are known by those skilled in the art as Type I and Type II, the main difference between them being that Type I contains less HMX (≦4%) and has a higher melting point (≧200° C.) than Type II (% HMX=4-17, melting point ≧190° C.) (Military specification: MIL-DTL-398D). RDX Type I and Type II are approximately identical to what a German specification (“Technische Lieferbedingungen 1376-802” (TL-1376-802)) describes as Type A and Type B respectively. RDX crystals contain slightly less energy, but are generally more stable and substantially cheaper to produce than HMX crystals.
From the point of view of safety, sensitivity to external influences is obviously an extremely important parameter for ammunition, and several countries have introduced requirements with regard to this. These are referred to as IM requirements (IM=Insensitive Munition). In order to attain these IM requirements, demands are also placed on the explosive employed in the ammunition. An important parameter in this respect is sensitivity to external heat influence. This parameter can be tested by means of the Fast Cook-off test. This Fast Cook-off test can be implemented by placing a pressed charge in a steel tube and sealing it at both ends. It is then heated rapidly until a reaction occurs, causing the tube to open. The reaction is graded from a Type I reaction to a Type V reaction. A Type I reaction will be a full detonation where the tube is split into many small fragments and a Type V reaction will mean that the tube is only cracked as a result of a pressure reduction. According to a German standard for low-sensitivity explosive (“Technische Lieferbedingungen 1376-800”) (TL-1376-800) the explosive is required to produce only Type V reactions.
When RDX or HMX are employed in ammunition, there are pressed into charges in order to achieve maximum density and thereby achieve maximum effect from the explosive. There will always be a certain risk involved in pressing explosive, and therefore every attempt is made to apply the lowest possible pressing pressure, generally referred to as improved pressability. Another advantage with improved pressability is that it will offer the producer the possibility of making much larger charges than is the case with explosive of inferior pressability. This will provide economic gains, particularly since alternatives to these large charges will involve the use of far more expensive production processes (castable/hardenable and meltable/hardenable processes).
It has been known for quite some time that in order to stabilise RDX and HMX crystals and make them suitable for pressing into charges, the crystals can be coated with a stabilising substance. To begin with different variants of wax were mainly employed for coating the crystals. Subsequently, more plastic materials have been employed, and in recent years compositions have been developed with more elastic plastic materials.